Production of pure titanium and zirconium



Dec. 4, 1956 I J. P. LEVY EEBDUCTION OF PURE TITANIUM AND ZIRCONIUMFiled Feb. 18, 1953 Invent-or g m 25ml. m w

A1 Attorneys PRODUCTION OF PURE TITANIUM AND ZIRCONIUM Joseph PeppoLevy, Acton, London, England Application February 18, 1953, SerialNo.337,475

Claims. (Cl. 266-33) This invention relates to the production oftitanium metal in a high state of purity.

Titanium is readily produced in the form of a volatilizable chloride bydirect reduction of its ore with carbon in the presence of chlorine, butthe production of the pure metal from the chloride is a matter ofconsiderable difiiculty owing to the great aflinity of the metal forother substances, more particularly for its afiinity for both the oxygenand nitrogen of the atmosphere and carbon and hydrogen. Even traces ofimpurities,particularly oxygen and nitrogen, may render the metalbrittle and unworkable and of much less commercial value, although themetal is of great utility when in the pure condition.

Many processes have previously been suggested for obtaining puretitanium from the tetrachloride. Thus, it has been previously suggestedto obtain titanium by reatent acting magnesium with titaniumtetrachloride in accordance with the formula 2TMg+TiCl4=2MgCl2+Ti byintroducing the titanium chloride vapour into molten magnesium, titaniumbeing retained in a matrix of unreacted magnesium and magnesiumchloride. It is extremely difficult, however, if not impossible, toremove all'occluded titanium tetrachloride vapour, and in the subsequentleaching of the mass with' water to remove magnesium chloride, thisresidual tetrachloride vapour is hydrolised, giving insoluble oxides andoxychlorides which cannot be subsequently removed without attacking thetitanium itself. Moreover, the leaching itself is a difficult operationto carry to completion and the titanium obtained by this process usuallycontains at least 1% of impurities, mainly because of the difliculty ofleaching the solid matrix. The use of hydrochloric acid may alsotitanium hydride and impurities in the material normally used for liningthe chamber may introduce further-impurities which contaminate thetitanium. i

It has now been found that titanium can be produced in a high state ofpurity without encountering the difiiculties above referred to if thereduction reaction is carried out in the vapour phase in the presence ofan inert gas (viz. one of the noble gases, in particular argon, heliumor neon, on account of their availability) to act as an entrainant andeffect the rapid removal and separation of the products of reaction, a

It is also essential, in order to avoid contamination by the walls ofthe reaction vessel of the titanium-metal when formed, to arrange forthe reaction to take place in a reaction zone surrounded by moving inertgas and to -carry away rapidly the reaction products as soon-as formedto a cool zone without contact while hot with the walls of the vessel,and also to prevent mist particles of alkaline earth chloride fromcoalescing.

It will be shown hereinafter that the employment of a vapour phasereaction in conjunction with a moving inert gas entrainant not onlyavoids the ditficulties hitherto encountered in obtaining pure titanium,but also carcurrent of titanium tetrachloride vapour.

A process for the production of pure titanium using a metal reducingagent consisting of magnesium con- I taining calcium is described andclaimed in my U. S. ap-

plication Serial No. 302,809, filed August 5, 1952, now abandoned,corresponding to British Patent No. 711,733, according to which thereducing agent is used in the molten or finely-divided solid state. Itwas found that the addition of calcium to magnesium, even in amounts of1 percent of calcium, has a marked scavenging or gettering elfect on theatmosphere in the reaction vessel, thereby contributing to the purity ofthe titanium liberated, the alloy preferentially absorbing hydrogen,oxygen, nitrogen and carbon.

Accordingly, in its broadest aspect, the present invention includes theprocess for the production of pure titanium which comprises reactingtitanium tetrachloride in the vapour phase and in the presence of amoving inert gas with the vapour obtained by'volatilising magnesium oran alloy of magnesium and calcium, by bringing together the vapours tobe reacted in .a reaction zone surrounded by the moving inert gas, andcollecting the reaction products in a finely-divided form by passing.them, while entrained in the inert gas, through a zone sufiicientlycoolto convert the metal chloride rapidly into solid form before theparticles are allowed to settle.

The inert gas employed may conveniently be argon on account of itsavailability and the employment of an 'alloy of magnesium and calciumhas the further advantage ofhigher reactivity and lower-melting pointthan rapidly away from the reaction zone. This is important as itenables the products of reaction to be maintained in finely-dividedstate in suspension until cool enough to be collected as a fine powderand it is this feature of the invention which enables the titanium metalto be separated from the magnesium chloride without the difficultiesreferred to above. Moreover, the inert gas acts to dilute the reactioningredients and thereby enables the strongly exothermic reaction to bebetter controlled. It also sweeps away excess tetrachloride vapour andthis is one of the many advantages of the use of a vapour phase reactionin conjunction with the employment of a moving inert gas. The highertemperature of the reaction provides a condition of greatly increasedchemical. activity. Furthermore, by reducing the tetrachloride withmagnesium vapour, the reaction becomes practically quantitative, becauseat that temperature'the products of reaction Ti+MgClz are in the solidand liquid phases respectively and can thus be easily carried away bythe entraining inert gas. This removal of the reaction products asrapidly as they are formed ensures that the reaction proceeds tocompletion and all the metal vapour .phase reaction using an entraininggas enables a continuous process in a closed cycle to be carried out.

In carrying out the invention, using the inert gas as a vehicle to carrythe magnesium vapour forward, it may be caused to draw the vapour from apool of boiling metal in a vessel surrounding the reaction Vessel bypassing it through a venturi and into the reaction vessel to meet aIdeal conditions obtain when the magnesium and titanium tetrachlorideare in stoichiometric proportions but a small excess of either reactantcan be tolerated and a slight excess of tetrachloride vapour over thatrequired to maintain molar proportions prevents the tetrachloride vapourfrom striking back and acting'on the surface of the pool of boilingmagnesium to form on the latter a cc'iati'n'gof metallic Chloride whichwould thus impede ebulli-tion of the metal. Any reaction on the moltenmagnesium moreover makes it necessary to separate and recover theproducts of such reaction with all the disadvantages hereinbeforementioned. The inert gas passing through the venturi exerts a valuablepumping action which enables the magnesium vapour to be carried into thereaction vessel very effectively.

The reaction is veryexothermic andthe radiated heat may be'utilised'inmaintaining the m'aghesiiimi'n a state of 'ebullition. v

The products of thereaetion'iare obtained in this way in the form of afinely-divided powder-consisting of magnesium chloride and titaniummetal as the result of the 'inertgasmoving the saidproducts to-a cool"zone 'in the apparatus and absorbin'g heat from them.

The deposition of both products 'of reaction in the form of "apowde'renablesthe metal-to be extractedwithout difficulty and upon reaching thecollecting vessel where for the firsttirne 'the reaction products comeinto contact with the walls '"of the vessel they are cool eneu h toremain uncontaminated.

Although argonis a comparatively expensive gasfthere is very little usedin the process, as the argon upenperforming its function 'rna'y berecirculated by passing through condensers and heat exchangers whic'hcool the gas 'andre'r'nove from it any excess tetrachloride. Thus, onlysmall proportions of gas require to be introduced into the circuit fromtime to time to make good small losses which may occur.

In view of the necessity for'keeping the molten magnesium out of contactwith either oxygen or nitrogen of the atmosphere, the magnesium boilermay be fed with molten magnesium from a second heated vessel "which isreplenished by billets of solid metal. The titanium tetrachlorideispressure-fed from a series of replenishedstorag e tanks 'and theproducts "of reaction are removed through an argon I lock at convenientintervals 'witho'ut'stopping the reaction.

The magnesium chloride can be easily removed and recovered from'thetitanium 'in'a condition which enables it to be economicallyreturned to electrolytic'cellsfor decomposition into metal andchlorinefboth of which can "be re-used in the process, 'for example,"bythe process "described ihfBr'itish 'patent ap lication No. 30,719/52,'file'd"December 3, I952, corresponding to my'co-pen di ng U. S.application Serial No. 395,610, filed December 1,

One 'spe'cific method of carrying out the -irivention in "a continuousmanner will 'now- 'be described with reference to the accompanyingdrawing, which shows diagramfniatilcally a form" of reaction vessel withits accompanying meltingj vessel for supplying moltenmagnesium ormagnesium-calcium allo'y.

v In the "drawing the reaction vessel 10 is in theform of a cylinder,the' sides' of 'which at the" top converge 'into'the -venturi throatllfthe upper part of the'reaction vessel 1 0" bei'ng surrounded byconcentric vessel 12 provided with acover 13 which maybeseciiredtotheflange '14 by bolts (not shown) or otherwise. :Thereaction vessel is"provide"d witha side inIe't'IS passinguhroug'h theouter vessel-'12. Above the outer"'vessel 12 is a small box 16 providedwith an inlet 17 and cover 19 through the bottom of whieh passesa tube20 extending upwardlynearly'to the'top of'the box 16 and downwardlythrough an aperture in the lid 13 terminating in a nozzle 21 situatedcentrally above theventuri throat 11. The outer vessel 12 communicatesthrough the -tube'22 "near the'bottom 'thereofl with theb'otto'mpart ofa melting vessel "23"closed' with cove-{24 in "which I is iifil ifi d an-i-nlet 25 of sufficient width -to take billets of magvessel 27. Bymeans of the valves 3 5, 36, 37, 38 and 39, the receiver can be shut oilfrom the rest of the apparatus for the purpose of uncoupling thereceiver and changing it withoutopening it or the apparatusvto-communication with the outside atmosphere.

In operation the outer vessel 12 and the melting vessel 23 are enclosedin furnaces (not shown) which melts the magnesium metal introduced intothe opening 26 and maintains the metal in 23 in a molten condition andthat in the outer vessel-12 at the boiling point. The apparatus may beworked as a continuous process in which argon from a suitable storage ispumped into the "box 16 at the inlet 17 I and passes through-a quantityof metallic calcium or other gettering material 18 and -enters the outervessel 12 through the delivery tubei20 and jet 21. The stream of argonemerging from the jet '21 and from thence into the venturi throat 11sets up -'a pumping action which draws magnesium vapour from above-themagnesium in the vessel 12 and carries-itdown the'reaction vessel 10where'it meets a stream of titanium -tetrachlon'de which enters throughthe inlet '15. An inten'se exothermic reaction is set up in thecentrepart of the reaction vessel 10 forming fine particles of titanium'metal and a mist of titanium tetrachloride-which is carrieddownwardsand enters the coolzone 27 in the lower part of the apparatuswhere the magnesium chloride solidifies in powder form and the mixedpowders are col- "lected in the receiver '30. Argoncontaining excesstetra- 'chloride passes out at 34 and enters a system of "condense'rsfor the removal of titanium tetrachloride which -isi pas'se'd to asuitable storage and the argon is re-circu- *la'ted entering theapparatus again at 17. By closing the -valves 35, 36,-"and'37, andopening valve 39, the receiver --rnay be changed 'pe'rio'dically byundoing the attachments at 32 and 29, the argon circulation beinguninterrupted through the short-circuiting valve 39.

V The level of the 'molt'en magnesium in the outer ves- -'sel 12 is keptconstant by addition of magnesium billets through the inlet 25 andtheconnection-22-enablesmolten anagnesium-to fl'ow'freely into the outervessel 1-2 Without "the air ente'ring the apparatus.

The following is' an exa'mple of an experimental batch carried out in anappara'tus as above described:

"A gas-fired .furnace was arranged to'pre melt 1 billets ofmagne'sinrn'in the melting Vessel-23 which could'convehie'ntly transferthe molten metal at about 850 C.to the boiler 12 heatedin e. secondsimilar furnace. ll) pounds of metal was I contained in the magnesiumboiler -12, the surface reaching to just below the venturi throat "11'which'ha's a diameter of' /2". The 'nozzle' 21 having a diameter 'ofwas situated'above the venturi= at -a distance suitable for drawing.into the reaction vessel 'magnesium'vapour by the argon which is passedthrough it. The "argon flow rate was 3 /2 cubic feet per minute and themagnesium evaporationwa's'fl pounds per'hour. The tit'a'niu'mtetrachloride corresponded tothe molar proportion 0f" 8 pounds per hourof magnesium. lnthis way the *gas flow was maintained at the optimum'value so that sufiicient magnesium "was drawn 'in to '"give apractically complete reduction 'of the titanium tetrachlof'ride duringits passage through the reaction "zone. Optimum conditionswill obviouslydependonmain'taining ,the correct adjustment of nozzle diameter,venturithro'a't "diameter, distance of "the nozzle-above the venturi andfate 'of argon-flow and magnesium. evaporation which reqiiire. previouscalculation and trial but .it I was'rfoun'd flifwith the apparatus use'dthe evaporation of magnesium metal conducive to the best result may varybetween 6 and 18 pounds per hour and the molar proportion of titaniumtetrachloride is introduced to correspond to the predetermined rate ofmagnesium evaporation desired during the course of any given experiment.Under the conditions stated above the product is delivered as a finediscreet powder and its particle size was measured for one experimentwhich was conducted and found to vary between 6 of an inch and of aninch.

It was also found that with the dimensions given above, anything under 2cubic feet per minute of argon gave rise to a solid matrix, and anythingabout 7 cubic feet per minute tends to give only partial reduction orscatters the product too rapidly in the apparatus to permit of cleansingof the argon.

Notwithstanding the fact that at the increased argon flow rate only apartial reduction is obtained, the reaction product is also of valuebecause under the influence of heat titanium dichloride may be made toyield titanium metal and titanium tetrachloride and the latter may beused for further reduction.

It has been found that an electrostatic or cyclone precipitatorinterposed in the argon circulating system is very effective incollecting the products of reaction and for the purpose of cleansing theargon from minute dust particles which it entrains.

I claim:

1. Apparatus for the production of pure titanium which comprises anupright reaction vessel, the upper part of which is surrounded by aclosed vessel for holding boiling magnesium, said reaction vesselconverging at the top above the level of the molten magnesium in theouter vessel in a venturi throat and disposed centrally above thelatter, an inlet pipe passing through the cover of the outer vessel andterminating in a nozzle, said inlet pipe being connected to a supply ofargon, the said reaction vessel being also provided with an inlet fortitanium tetrachloride passing through the sides of the outer vessel andthe reaction vessel and terminating within the latter at a point belowthe venturi throat, the lower part of the reaction vessel opening into acooling vessel and receiver, the said cooling vessel and the receiverbeing provided with an outlet for carrying away argon and excesstitanium tetrachloride.

2. In apparatus for the reduction of metal chlorides in the vapour phasewith a reducing metal in the presence of an inert gas, which apparatuscomprises a reaction chamber, the upper part at least of which issurrounded by a closed outer chamber, the said reaction chamberconverging at its upper end into a venturi throat and opening at itslower end into a cooling and collecting chamber; an

inlet conduit for the inert gas passing through the upper cover of theouter chamber and terminating in a jet nozzle situated centrally abo ethe venturi throat of the reaction vessel; an inlet conduit for metalchloride vapour passing through the side of the outer vessel andentering the reaction vessel at a point below the converging upper end.thereof; means for supplying the upper part of the outer vessel withreducing metal vapour, and a conduit connecting the collecting vesselwith means for recirculating the inert gas.

3. Apparatus as claimed in claim 2, wherein at least one cycloneseparator is interposed in the inert gas circulating system to collectthe products of reaction and cleanse the inert gas from minute dustparticles entrained therein.

4. In apparatus for the reduction of metal chlorides in the vapour phasewith a reducing metal in the presence of an inert gas, which apparatuscomprises a reaction chambar, the upper part at least of which issurrounded by a closed outer chamber, said reaction chamber convergingat its upper end into a venturi throat and connected at its lower endwith a cooling chamber which in turn is connected to a collectingchamber; an inlet conduit for the inert gas passing through the uppercover of the outer chamber and terminating in a jet nozzle situatedcentrally above the venturi throat of the reaction vessel; an inletconduit for metal chloride vapour passing through the side of the outervessel and entering the reaction vessel at a point below the convergingupper end thereof; means References Cited in the file of this patentUNITED STATES PATENTS 1,306,568 Weintraub June 10, 1919 2,205,854 KrollJune 25, 1940 2,551,341 Sc'heer et al. May 1, 1951 2,556,763 Maddex June12, 1951 2,564,337 Maddex Aug. 14, 1951 2,567,838 Blue Sept. 11, 1951FOREIGN PATENTS 296,867 Germany Mar. 13, 1917 386,621 Great Britain Apr.13, 193 1

1. APPARATUS FOR THE PRODUCTION OF PURE TITANIUM WHICH COMPRISES ANUPRIGHT REACTION VESSEL, THE UPPER PART OF WHICH IS SURROUNDED BY ACLOSED VESSEL FOR HOLDING BOILING MAGNESIUM, SAID REACTION VESSELCONVERGING AT THE TOP ABOVE THE LEVEL OF THE MOLTEN MAGNESIUM IN THEOUTER VESSEL IN A VENTURI THROAT AND DISPOSED CENTRALLY ABOVE THELATTER, AN INLET PIPE PASSING THROUGH THE COVER OF THE OUTER VESSEL ANDTERMINATING IN A NOZZLE, SAID INLET PIPE BEING CONNECTED TO A SUPPLY OFARGON, THE SAID REACTION VESSEL BEING ALSO PROVIDED WITH AN INLET FORTITANIUM TETRACHLORIDE PASSING THROUGH THE SIDES OF THE OUTER VESSEL ANDTHE REACTION VESSEL AND TERMINATING WITHIN THE LATTER AT A POINT BELOWTHE VENTURI THROAT, THE LOWER PART OF THE REACTION VESSEL OPENING INTO ACOOLING VESSEL AND RECEIVER, THE SAID COOLING VESSEL AND THE RECEIVERBEING PROVIDED WITH AN OUTLET FOR CARRYING AWAY ARGON AND EXCESSTITANIUM TETRACHLORIDE.